Ni-Based single crystal superalloys are used for members to be used under high temperatures and high stresses, such as turbine blades, turbine vanes, etc. in jet engines, gas turbines, and the like. In recent years, in gas turbine engines represented by jet engines and the like, in order to enhance output and efficiency, an inlet gas temperature of the turbine is made higher. Then, in order to keep high-temperature strength, turbine blades or turbine vanes of gas turbines have a hollow blade structure and prevent a temperature increase of a base material by forced cooling of the blade interior. However, a surface temperature of the blade of turbine blades or turbine vanes exceeds 900° C., whereas an internal temperature of the blade is about 600° C., so that a temperature difference between the surface and the interior of such a blade generates TMF.
In addition, the turbine blades are rotated at a high speed during being exposed to a high-temperature combustion gas and a centrifugal force is applied thereto, and therefore, they must endure a high-stress creep. Similar to TMF characteristics, creep characteristics are also important characteristics for the Ni-based single crystal superalloys. Examples of a cause of deteriorating the creep characteristics or TMF characteristics include precipitation of a TCP phase (topologically close packed phase), and in particular, a problem thereof is visualized in long-term use at high temperatures.
As for the Ni-based single crystal superalloys, PWA1480 (a trademark) or those described in PTLs 1, 2, 3, 4, and 5 as described below are known. However, these Ni-based single crystal superalloys are not sufficient in creep characteristics to contemplate increase of the efficiency by making a combustion gas temperature of the gas turbine higher. Then, Ni-based single crystal superalloys described in PTLs 6, 7, and 8 as described below, which contain expensive Re, appeared. However, as for the Re-containing Ni-based single crystal superalloys, when applied to large-sized members, a problem that the material costs are excessively expense is pointed out.
In addition, in the Ni-based single crystal superalloys, orientation dependence in which a deviation of angle in the <001> crystal orientation under high stresses largely influences the strength also becomes problematic. Small orientation dependence means that waste of manufacturing members becomes small. For this reason, the small orientation dependence is more advantageous as the size of the member is larger, and it may be considered that such is excellent in cost performance from the standpoint of practical use.